I've killed thousands upon thousands of those things, and I got a blue Magma shield ONCE. And it was 15 armor. Shit, the white ones are always max armor. Go figger. Titans are best for rune and material farming. After a full run (~120 titans) you'll have a nice stack of wood, iron, and steel, and quite a few runes that may or may not be of any use. I usually get 2 or 3 lockpicks and an ele tome as well.
After Hard Mode came about, I did get a gold Magma Arm (hammer) to drop, so maybe there's hope for that elusive shield, but don't hold yer breath.
Edit: Ha, I eat my words today, actually got a max purple shield to drop (haven't ID'ed it yet), among other things. Killed about 130 of them in this run (popups vary the total), and got the haul below:
I think 7 gold runes is my personal record for a single run. Money doesn't drop much anymore, but definitely more purps and golds.